Spray degasser

ABSTRACT

The present invention relates to a spray degasser for removing gas from a liquid, comprising: 
     i) a boiler having at least one sprayer compartment, 
     ii) the sprayer compartment comprises a radial sprayer which is connected to a liquid feed for spraying the liquid for degassing as a spray screen over the liquid present in the boiler, 
     iii) a feed pipe for feeding into the liquid present in the boiler vapour to create in the sprayer compartment a gas containing vapour, 
     iv) an outlet in the sprayer compartment for venting the gas removed from the liquid, and 
     v) an outlet in the boiler for degassed liquid.

The invention relates in particular to a spray degasser for removingoxygen from water. Oxygen is an important factor which can result incorrosion in steam boilers and turbines. The problem of corrosion occursparticularly when work is done at high temperatures and pressures. Usinga degasser the oxygen content in the water must be reduced in general toless than 10 ppb, preferably to less than 5 ppb.

In a known spray degasser the gas is separated from liquid in two steps.A first step is the so-called "scrub" step, wherein steam and water arebrought into contact at generally equilibrium temperature and pressure,wherein the steam has a very low oxygen partial pressure. The water isdegassed with this steam. The second step is the "heating" step, whereinalmost all the steam condenses into water which is sprayed as a sprayscreen, wherein the water is brought to the equilibrium temperature. Asmall portion of the steam is discharged via an outlet using thereleased gases which do not condense under these conditions (see"Deaerating boiler feed water--The theoretical background" by G. S. Soltand W. Wiemer, and "The Stork spray type deaerator: design, developmentand experience" by W. Wiemer and G. S. Solt in Symposium on Degassing,15 June 1978, pages 49-56 and 57-70 respectively).

A spray degasser with a radial sprayer is described for instance inFR-A-2 379 753.

U.S. Pat. No. 2,379,753 describes a water treatment and degassingapparatus having a series of annular cone sprayers in tangentiallyslanting arrangement for the purpose of generating a powerful waterrotation in the underlying liquid. The cone-like spray screens aresurrounded by a cylindrical partition. Steam can only pass laterallythrough the spray screens and via short-circuit openings between twoadjoining cone spray screens and the partition into the space situatedthereabove.

It will be apparent that the level of the partial oxygen pressure in thespace above the spray screen determines the operation of the spraydegasser. An improvement of the degassing action can be obtained by afurther lowering of the partial oxygen pressure therein, which howeverrequires an increase in the quantity of steam to be blown off, which isattended by greater heat losses.

Further research into a spray degasser has shown that the partial oxygenpressure of steam which passes through the spray screen islocation-dependent. The temperature in the spray screen increases namelyfrom the place where the spray screen is formed as a result of thecondensation of steam passing therethrough. Steam which passes throughthe spray screen at a lower temperature will be richer in oxygen afterpassing through the screen than steam which passes through the sprayscreen at a higher temperature. By separately collecting the steamrelatively enriched with oxygen and then blowing this off, the degassingaction of the spray degasser can on the one hand be improved with thesame quantity of blown off steam, thereby obtaining deeper degassing,while on the other hand, for the same degree of degassing, it cansuffice to blow off a smaller quantity of steam, thereby reducing heatlosses.

A spray degasser according to the invention is characterized in that thesprayer compartment comprises a gas compartment above and adjoining thecolder spray screen, delimited by a gas compartment wall extending froma boiler wall to the colder spray screen, onto which the outlet in thesprayer compartment connects.

It is noted that steam which passes through the spray screen at a warmerlocation can also reach this compartment by again passing radially incounterflow through a spray screen that is becoming colder and as aresult of further condensation reaches the compartment enriched withoxygen.

According to a preferred embodiment the compartment surrounds thesprayer.

In a practical embodiment the separating means comprise a compartmentwall which extends from a boiler wall to the spray screen.

If in preference the compartment wall is provided at its free end facingtowards the spray screen with a foot extending along the spray screen,the passage of steam is elongated radially in counterflow through thespray screen towards the compartment, which is associated with a furtherenrichment with oxygen. The foot preferably extends beyond thecompartment.

Since the spray screen has a lowest temperature immediately afterleaving the sprayer, and steam which passes through the spray screen atthis location is thereby maximally enriched with oxygen, it isrecommended that the compartment is located at a short distance from thesprayer.

If the spray screen has no splash plate or plates bounding itsperiphery, or if the steam passing radially through the spray screenmust preferably be further enriched with oxygen, it can be advantageousif the degasser contains in addition to the first compartment another,second compartment which likewise adjoins the spray screen and adjoinsthe first compartment on the other side.

For constructional reasons it is recommended that the second compartmentsurrounds the first compartment.

Mentioned and other features of a spray degasser according to theinvention will hereafter be better comprehended from the followingdescription of a number of non-limiting embodiments of spray degassersaccording to the invention which are only given by way of example and towhich the invention is in no way limited. In respect of theseembodiments reference is made to the drawings, in which

FIG. 1 shows a flow diagram for an electricity power stationincorporating a spray degasser according to the invention;

FIG. 2 shows a perspective partially broken away view of a spraydegasser according to the invention from FIG. 1;

FIG. 3 is a section along the line III--III from FIG. 2;

FIGS. 4, 5 and 7 show sections corresponding with FIG. 3 of otherembodiments; and

FIG. 6 is a perspective view of a variant of detail VI from FIG. 2.

FIG. 1 shows a flow diagram for an electricity power station whichcomprises a steam boiler 1, a turbine 2, a condenser 3, a low pressureheating unit 4 which is connected to the condenser 3 via a pump 5, and ahigh pressure heating unit 6 which is provided with degassed water viathe pump 7.

The spray degasser 8 according to the invention is situated between thelow pressure heating unit 4 and the pump 7.

The spray degasser 8 (see FIG. 2) comprises a boiler 9 partially filledwith liquid 10, in this case water. Reaching into the water 10 are steampipes 11 which are provided in the portion thereof protruding into thewater with holes out of which steam enters the liquid. The steam pipes11 are connected to a steam conduit 13 which is connected to a vapourfeed 14, in this case a steam feed 14, which is connected to the turbine2.

The boiler 9 is further provided with spray means 15 which comprise aper se known sprayer 16 with which is formed a number of spray screens17 lying one above the other. The spray means 15 further comprise a feed18 for liquid for degassing which is connected to the low pressureheating unit 4.

In addition the boiler 9 is provided with an outlet 19 for degassedliquid and, finally, with outlets 20 for discharging removed gas intothe atmosphere. Finally, it is possible via the pipe 121 to carrycondensate from the high pressure heating unit 6 back to the degasser 8.

The spray degasser 8 according to the invention will be discussed inmore detail with reference to FIG. 3.

Using the sprayer 16 a number of spray screens 17 are generated whichare bounded on their periphery by a splash screen 21 and concentricsplash rings 22 and 23 arranged thereon, from which the water fallsdownward.

Using separating means 24 according to the invention, in this case usinga compartment wall 25 which reaches to the top spray screen 26 withoutthereby substantially coming into contact therewith, a compartment 27 isseparated from the space above the spray screens. The spray screens 17,26 have a colder region 17a proximal to the sprayer 16 and a warmerregion 17b distal to the gas compartment wall 25. The outlets 20 for gasremoved from the liquid debouch into this compartment 27. Steam 124which is injected via the steam pipes 11, can reach the compartment 27directly after passing through the spray screens 17, 26. Steam 28 whichhas entered the remaining space 29 via the warmer spray screen portions,can reach the compartment 27 indirectly by going under the compartmentwall 25 through the colder spray screens as according to the arrow 30.Steam thus enters the compartment 27 which is relatively rich in gasremoved from the liquid, in this case oxygen.

FIG. 4 shows a degasser 31 according to the invention. In this case theseparating means 24 according to the invention comprise a compartmentwall 32 which separates the compartment 27 around the sprayer 16, and isprovided at its end 33 facing towards the spray screens 17, 26 with afoot 34 which extends along the spray screen 26 into and outside of thecompartment 27, while the spray screen 26 is not substantiallydisturbed. Steam which enters the compartment 27 indirectly as accordingto the arrow 30 is thus constrained to opt for a longer path throughcolder spray jet portions.

FIG. 5 shows a spray degasser 135 according to the invention in itsmost-simple form. Omitted in this case are means for bounding the sprayscreens 17 and 26, in particular the splash screen 21 and the splashrings 22 and 23, The advantages according to the invention cannevertheless be obtained because the compartment 27 from which gasseparated from the liquid is removed via the outlets 20 is separated offaround the sprayer 16, using a compartment wall 35 at a short distancetherearound.

FIG. 6 shows another spray degasser 36 according to the invention withwhich a compartment 27 is separated of around the sprayer 16 using thecompartment wall 25 comprised of the separating means 24. In this casethe separating means 24 according to the invention comprise a secondcompartment wall 37 with which a second compartment 38 is separatedaround the first compartment 27. Further omitted is the splash screen 21but splash rings 39, 40 and 41 are retained. Preferably only gas with asmall quantity of steam is removed from the compartment 27. If desired,it is likewise possible to discharge gas-enriched steam out of thecompartment 38 via the gas outlets 42 and 43.

Finally, FIG. 7 shows a spray degasser 44 according to the invention.The compartment 45 has the form of an annular container 46 open to thebottom, which surrounds the sprayer 16. The sprayer 16 extends throughand beyond a central container opening 4. An outer peripheral edge 48 isprovided at the free end 49 with a foot 50. The container is fixed tothe outlets 20. The container 46 thus hangs free of the boiler 9 abovethe spray screen 26.

Although the spray degasser is only described for degassing water incombination with its vapour phase steam, it will be apparent that otherliquids can also be degassed insofar as use can be made of their vapourphase. For example, lower alcohols can be degassed in the same manner ofnon-condensing gases, such as oxygen, nitrogen and the like.

I claim:
 1. A radial spray degasser for removing noncondensable gas froma liquid to be degassed, the degasser comprising:(a) a boiler having aboiler structure; (b) an inner spray compartment, the spray compartmentlocated in an upper portion of the boiler, the spray compartmentcomprising:(i) a surrounding wall defining the inner sprayercompartment, the wall extending downward from the structure of theboiler so that lower edges of the wall are in contact with an upperportion of a spray screen of liquid being degassed when the degasser isin use; (ii) a radial sprayer located within the inner spray compartmentat a distance from and surrounded by the surrounding walls, the sprayerhaving a first end and a second end, the first end connected to an inletconduit for supplying liquid to be degassed to the radial sprayer, thesecond end extending into the inner spray compartment with liquidoutlets, for spraying of liquid to be degassed radially outward in aspray screen, located above the lower edges of the surrounding wall; and(iii) an outlet extending from an upper portion of the inner spraycompartment for venting noncondensable gasses that accumulate in saidcompartment; (c) an outer compartment defined by walls spaced from andsurrounding the inner compartment, the walls of the outer compartmentextending downward from the boiler structure, said walls of sufficientlength to intercept an outer circumferential edge of the spray screen ofthe radial sprayer, said walls of the outer compartment extendingfurther downward into the boiler than the surrounding walls of the innersprayer compartment; (d) steam pipes having perforated lower extremitiesextending into the boiler such that the perforated extremities aresubmerged in liquid and steam exiting from the pipes is able to bubblethrough the liquid and travel upward to the spray screen to degas liquidof said spray screen when the boiler is in use; and (e) an outlet of theboiler for removing degassed liquid from the boiler; whereby, when thedegasser is in use, steam containing noncondensable gasses stripped fromthe liquid accumulates in a space between the walls of the inner spraycompartment, and the distance between the radial sprayer and thesurrounding walls of the inner spray compartment is such that steam andgasses crossflow from the outer compartment through the spray screen ofliquid into the inner spray compartment, the liquid thereby undergoingfurther degassing, before the gasses vent from the degasser.
 2. Theboiler of claim 1, wherein a foot extends along the lower edges of thewalls of the outer surrounding compartment, the foot angled so that aspray screen from the radial sprayer is not substantially disturbed andso that steam and noncondensable gasses entering the inner compartmentfrom the outer surrounding compartment are constrained to travel aroundthe foot.
 3. A radial spray degasser for removing noncondensable gasfrom a liquid to be degassed, the degasser comprising:(a) a boilerhaving a boiler structure; (b) a single sprayer compartment disposed inan upper portion of the boiler, the sprayer compartment comprising:(i) asingle surrounding wail defining the compartment, the wall extendingdownward from the structure of the boiler so that lower edges of thewall are in touching relation with an upper portion of a spray screenwhen the degasser is in use; (ii) a radial sprayer located within theinner spray compartment and a distance from the wall, the sprayerextending downward into the compartment for spraying liquid to bedegassed as a spray screen radially outward and downward, the liquidoutlets of said sprayer located at a level above the lower edges of thewalls defining the compartment; and (iii) an outlet from the compartmentfor venting noncondensable gasses accumulating in the compartment, whenthe degasser is in use; (c) steam pipes having perforated lowerextremities extending into the boiler so that the perforated extremitiesare submerged in liquid and steam exiting from the pipes is able tobubble through the liquid and travel upward to the spray screen to degasliquid of said spray screen when the boiler is in use; and (d) an outletextending from the boiler for removing degassed liquid from the boiler;whereby, when the degasser is in use, a portion of steam andnoncondensable gasses stripped from the liquid being degassed areconstrained, due to the distance between the radial sprayer and thesurrounding wall, to crossflow beneath the walls of the compartment,counter to the spray screen, thereby causing the steam andnoncondensable gasses to contact a coldest portion of the spray screento further strip gasses from the liquid and condense steam.
 4. A radialspray degasser for removing noncondensable gas from a liquid, thedegasser comprising:(a) a boiler having a boiler structure; (b) a radialsprayer extending downward into an upper portion of the boiler, thesprayer able to spray liquid to be degassed in a spray screen radiallyoutward and downward; (c) two spaced apart walls defining an annularspace between, the space capped with a roof to form a compartment, thewalls surrounding the radial sprayer and spaced from said sprayer, awall further from the sprayer extending further downward into the boilerthan a wall closer to the sprayer, the wall closer to the sprayer spacedfrom the sprayer, both of said two spaced apart walls extending downwardsuch that lower edges of the walls touch a spray screen from the radialsprayer, when the degasser is in use; (d) steam pipes having perforatedlower extremities extending into the boiler such that the perforatedextremities are submerged in liquid and steam exiting from the pipes isable to bubble through the liquid and travel upward to the spray screento degas liquid of said spray screen when the boiler is in use; (e) avent for nondensable gasses extending through the roof of thecompartment to vent gasses to outside the boiler; and (f) an outlet ofthe boiler for removing degassed liquid from the boiler.